2. QUESTIONS
1. Name the 3 layer of the Sun’s atmosphere. Corona,
chromosphere and photosphere
2. Which layer of the Sun’s atmosphere can only be seen in a total
eclipse of the Sun? Why? Corona and
chromosphere, because they are not bright
enough
3. Why do sunspots appear to move across the Sun’s surface from
the west to the east? Because the Sun rotates from
west to east
3. QUESTIONS
4. What causes aurorae in the Earth’s north and south poles?
Charged particles deflected to the poles of the
Earth by the Earth’s magnetic field collide with air
molecules
5. How is heat generated in the Sun’s core? By
thermonuclear reaction in the core
4.
5.
6.
7.
8.
9.
10. STARS
A star is a natural hot ball of gases in
space which gives out its own heat
and light
A star is usually made up of almost
entirely of hydrogen and helium
11.
12. STARS
A star gets its heat and light from
thermonuclear reactions.
A thermonuclear reactions happens
when the hydrogen atoms of a star
combine to form helium atoms. This
process releases plenty of heat and
light.
17. SUN’S ENERGY: NUCLEAR FUSION
When the star’s core gets hot enough (millions of
degrees) Nuclear Fusion starts.
Hydrogen + Hydrogen Helium + ENERGY (+ neutron)
Fusion continues to make heavier & heavier elements.
Stops at Iron
18.
19. NUCLEAR FUSION
Nuclear Fusion is the process that releases energy on stars. It
takes place in the core of the star.
It starts when gravity pulls nebula together and temperatures
increase to millions of degrees.
In nuclear fusion, the nuclei (protons and neutrons) of atoms
fuse together to make heavier elements and release energy.
H + H Helium + (neutron) + ENERGY
20. STARS
Stars are huge balls of hot gases. But
they look small to us because they
are very far way.
The distance of a star from the Earth
is measured in light years
One light year is the distance light
travels in one year (light travels at
300 000 km/s)
21. STARS
One year = (300,000 X 60 X 60 X 24
X 365) km =9,460,800,000,000 km
9,500,000,000,000km
22. STARS
After the Sun, the nearest star is Alpha Proxima. It is about 4.2 light
years away and can only be seen through a telescope.
Proxima Centauri, the nearest known
star to our solar system, is shown here
in an image taken on April 6, 2007, at
15:12 UTC. This is a composite of 3
exposures each 30 seconds long
through I (infrared), R (red), and V
(visible) photometric filters. The image
was rendered in SAOImage ds9 with
red, green and blue corresponding to
those three filter bands. For the 650x480
pixels in this cropped image, the field of
view shown is 5.8x4.3 arc minutes with
north up and west to the right. Proxima
is the 11.05 V magnitude spectral type
M5.5V red star at the center.
23.
24.
25. ALPHA CENTAURI (半人马座阿尔法星)
Alpha Centauri is 4.3 light years away from the Earth, but it can
be seen with the naked eye.
26. STARS
Two very bright
stars which can be
easily be identified
are Sirius (天狼星)
and Rigel (猎户座
-参宿七)
27. STARS
In ancient times,
travelers used
stars to guide
them in their
journeys across
the deserts and
the seas.
28.
29.
30.
31.
32.
33.
34.
35.
36. CLASSIFICATION OF STARS
Stars can be classified according to
their characteristics such as:
Temperature and colour
Brightness
Chemical composition
Size
density
38. 1. TEMPERATURE AND COLOUR
The temperature of a star affects it
colour.
The hottest star is blue while the
coolest is red
Blue stars are young stars
Red stars are old stars which are
cooling
40. 2. BRIGHTNESS
Stars can be
classified according
to their brightness.
The brightest star,
i.e. the Sun, has a
magnitude of -26.5
The dullest star is
given a magnitude
of +26.0
The brighter the
star, the lower its
magnitude is
46. 3. CHEMICAL COMPOSITION
Most stars are composed of hydrogen and
helium
Some stars contain other elements such
as iron and carbon
47. Spectra - Jan 1, 2007
This image (hi-res version) shows absorption lines in the sun's visible
spectrum. To find out more, see Atomic Absorption and Emission Spectra.
48. Analysis of these lines determines the chemical composition of a star. For an
explanation of why the lines of calcium--rather than hydrogen--dominate the
solar spectrum, go to "Analysis of absorption Lines" in Spectra, from the
University of Illinois (the other sections are interesting, too).
50. 4. SIZE
Stars vary a great deal in size
White dwarfs are smaller than the
Earth
Red giants are about 100 times
bigger than the Sun
Supergiants are about 400 times
bigger than the Sun
51.
52. 5. DENSITY
The densities of stars vary a lot because of their sizes
A big star has a low density (density = mass/volume)
The spiral arms are thought to be areas of
high density matter, or "density waves". As
stars move through an arm, the space
velocity of each stellar system is modified
by the gravitational force of the higher
density. (The velocity returns to normal
after the stars depart on the other side of
the arm.) This effect is akin to a "wave" of
slowdowns moving along a highway full of
moving cars. The arms are visible because
the high density facilitates star formation,
and therefore they harbor many bright and
young stars.
53. The spiral arms are thought to be areas of high density matter, or "density waves". As stars move through
an arm, the space velocity of each stellar system is modified by the gravitational force of the higher
density. (The velocity returns to normal after the stars depart on the other side of the arm.) This effect is
akin to a "wave" of slowdowns moving along a highway full of moving cars. The arms are visible because
the high density facilitates star formation, and therefore they harbor many bright and young stars.
56. FORMATION OF STARS
Stars are constantly being formed in outer space
Scientist believe that a star is formed from a nebula (星云)
57. FORMATION OF STARS
A nebula is a large cloud of dust and gas, mainly hydrogen, in
outer space.
The dust and gas in the nebula condense and become
compressed due to the gravitational attraction of the particles
58. FORMATION OF STARS
The compressed dust and gas become very
hot and dense until a very high temperature is
reached.
The very high temperature causes
thermonuclear reactions to take place. In a
nuclear reaction, hydrogen atoms combine or
fuse together to form helium atoms
59. FORMATION OF STARS
This nuclear reaction produces a tremendous
amount of heat and light. So the ball of dense
compressed dust and gas gives out its own
heat and light. Thus a star is formed.
A star takes millions of years to form.
60.
61.
62. DEATH OF STARS
When the hydrogen in a star is used
up, the nuclear reactions in the star will
stop
The star will cool and eventually die
When a star dies it will leave behind:
A white dwarf,
A neutron star, or
A black hole
63.
64. 1. WHITE DWARF
When a star of similar size as the Sun has almost completely
used up its hydrogen, the outermost layer of hydrogen burns
fiercely and causes the star to expand.
The star becomes red and is called a red giant.
65. 1. WHITE DWARF
The outer layer of the red giant is unstable and diffuses into
space.
The inner gases collapse and form a hot core known as a white
dwarf
66.
67. 1. WHITE DWARF
A white dwarf is about the size of the Earth
Eventually the white dwarf cools and does not give out heat and
light. It becomes a black dwarf in space
68.
69.
70. 2. NEUTRON STAR
If a dying star is about 10 times the size of the Sun, it expands
and becomes a red giant.
The red giant formed is very big.
71. 2. NEUTRON STAR
The inner gases collapse so quickly that the red giant explodes,
causing a supernova explosion
72.
73. 2. NEUTRON STAR
The remaining core shrinks with such force that the electrons and
protons combine to form neutrons.
The core left is called a neutron star
74. 2. NEUTRON STAR
A neutron star:
has a mass of 1.5 and 2.5 times the
mass of the Sun
Is very dense (because of its
neutrons)
Rotates very fast
Releases pulsing electromagnetic
waves (because of this, it is also
called a “pulsar” 脉冲星)
75.
76.
77. 3. BLACK HOLE
A black hole is formed from a very big red giant. It is called a
supergiant.
A supergiant has a size of about 500 times the size of the Sun.
78. 3. BLACK HOLE
The explosion of a supergiant causes a gigantic supernova explosion.
The core left is so dense and its gravitational force is so great that it
attracts even light.
79. 3. BLACK HOLE
The attraction of light by the core makes the region around it dark.
Hence the core is called a black hole
A black hole cannot be seen but its effect can be felt
80.
81.
82.
83.
84. CONSTELLATIONS
A constellation is a group of stars which forms a particular pattern
that can be seen from the Earth.
Astronomers have recognized 88 constellations.
85. CONSTELLATIONS
Some constellations can be seen throughout the year, while some
can be seen only at certain times of the year. This is because the
Earth is revolving around the Sun.
86. CONSTELLATIONS
In ancient times, people used these constellations
to guide them in their journeys and to tell the
seasons.
12 of the constellations form the zodiac. This
name means the path of the animals, because
many of the constellations are named after
animals.
87.
88.
89.
90.
91. GALAXIES
A galaxy is an assembly of millions of stars in outer space.
The stars in a galaxy revolve around the centre of the galaxy.
92. GALAXIES
Galaxies can be classified according to their shapes:
Spiral
Elliptical
Irregular
Barred spiral
95. 1. SPIRAL GALAXY
Examples are the Milky Way (银河系) and the
Andromeda (仙女座)
A spiral galaxy is very large
It has a thick bright centre and thins out at the
edge
The centre has more stars which are older those
at the edge.
97. 2. ELLIPTICAL GALAXY
It is the most common type of galaxy
It is smaller than a spiral galaxy
It consists of very old stars
It cannot form new stars because it
does not contain any more dust and
gas.
Elliptical Galaxy M87
98. 3. IRREGULAR GALAXY
Utah Skies
Challenge
Object, Irregular
Galaxy
NGC1275(mag11.6)
Irregular Galaxy
NGC1275 and
neighbors This
galaxy is located
near the center of
the Perseus Galaxy
Cluster -- a group of
some 530
members.
Depending on the
size of your
telescope and the
quality of your
skies, you'll see
many, many
galaxies clumped
together in this
99. 3. IRREGULAR GALAXY
It does not have a fixed shape
It can form new stars because it possesses dust and gases
(nebula)
It consists of young stars
100. Big, beautiful, barred spiral
galaxy NGC 1300 lies some 70
4. BARRED SPIRAL GALAXY million light-years away on the
banks of the constellation
Eridanus. This Hubble Space
Telescope composite view of the
gorgeous island universe was
released at this week's meeting of
the American Astronomical Society
as one of the largest Hubble
images ever made of a complete
galaxy. NGC 1300 spans over
100,000 light-years and the
Hubble image reveals striking
details of the galaxy's dominant
central bar and majestic spiral
arms. In fact, on close
inspection the nucleus of this
classic barred spiral itself shows a
remarkable region of spiral
structure about 3,000 light-years
across. Unlike other spiral
galaxies, including our own Milky
Way, NGC 1300 is not presently
known to have a massive central
black hole.
101. 4. BARRED SPIRAL GALAXY
This type of galaxy is uncommon
It has a cross-like formation in the centre
108. THE MILKY WAY
Our Solar System belongs to a galaxy called the Milky Way
The Milky Way is a spiral galaxy
It contains about 10,000 million stars together with dust and
gases.
It is very big. It takes 100,000 light years to cross its diameter
109. THE MILKY WAY
The Solar System is located towards the edge of the galaxy
The Sun rotates from west to east and at the same time, orbits
the centre of the Milky Way